Adsorption and oxidation of carbon monoxide on a rhodium electrode studied by in-situ infrared spectroscopy

Abstract

The infrared spectra of linear and bridge CO adsorbed on a Rh electrode have been determined as a function of the potential in 0.5 M H 2SO 4 and 0.2 M K 2SO 4. In the neutral medium, the ratio of the integrated band intensities, bridge/linear (0.82), is independent of the potential throughout the potential region between 0 and 0.85 V (vs. RHE). This indicates that the surface density of bridge CO(a) is almost comparable to that of linear CO(a). In the acidic medium, however, the ratio decreases continuously from 0.75 to 0.5 between 0 and 0.6 V (vs. RHE). The rates of the C-O stretching frequency shift with the potential of the linear and bridge CO(a) are 40 and 36 cm t1̄ /V, respectively, in 0.5 M H 2SO 4, and 60 and 50 cm −1 /V in 0.2 M K 2SO 4, respectively. The effect of UPD Cu adatoms on the nature of the adsorbed CO was investigated by observing the infrared spectra of CO(a) in the absence and presence of Cu adatoms (surface coverage = 0.2). It was found that bridge CO(a) is selectively removed by the UPD Cu adatoms, but electrochemical desorption of Cu adatoms is greatly retarded in the presence of the adsorbed CO layer, while oxidation of the adsorbed CO is accelerated by the UPD Cu adatoms.